1. Field of the Invention
The present invention relates generally to a tip unit for a liquid applicator such as a water-based ball-point pen, and also a method of producing thereof. The invention also relates to a ball-point pen tip unit allowing liquid to be discharged in a relatively large rate and a method of producing thereof. In this specification, the writing instrument is considered as a kind of ink applicator in the broad meaning of the word.
2. Background Art
A liquid applicator having a ball placed into its distal part is conventionally known, wherein the ball transfers liquid, which adheres to the ball, onto the surface to be applied by being pressed. A typical example is a ball-point pen, which uses ink as the liquid. Inks of various kinds such as dyes or pigments dispersed in water, called “water-based inks” are known, as well as “water-based ball-point pens” containing such inks. “Water-based gel inks”, i.e., gelatinized inks are also used. Some ball-point pens using water-based gel ink can deliver a relatively large rate of ink.
The tip unit incorporated in the ball-point pen includes a ball for writing rotatively retained in a tip body, and while the ball-point pen is used, the ball rolls to transfer the ink from an ink reservoir to the writing surface such as a paper through the ball.
The known tip unit used in the ball-point pen will be described:
Referring to FIG. 17A, which is a cross-section showing the distal end of a tip unit 120, the tip unit 120 is mainly composed of a tip body 100 and a ball 102. The distal end of the tip body 100 is shaped like a truncated cone. The ball 102 is retained in a ball housing (a socket) 103, and is held by the distal end 101 of the tip body 100.
The tip body 100 is provided with the ball housing 103 shaped in concave at its distal end, and a capillary hole 110 at its proximal end. The ball housing 103 is provided with a ball resting seat or merely seat 105 having a conical inner surface. The tip body 100 is further provided with ink channels 107 each communicating with the seat 105. The ink channels 107 secure smooth flow of liquid when the ball-point pen is used. The liquid flows toward the distal end 101 through the capillary hole 110 along the ink channels 107. This construction keeps the liquid flow even with the ball 102 pushed toward the seat 105 in using the ball-point pen, so as to apply the liquid.
Referring to FIG. 18, the flow of liquid in writing with the ball-point pen will be described:
In using the ball-point pen, the liquid in the tip unit 120 flows through the ink channels 107 via the capillary hole 110, and reaches the ball housing 103 through outlets 107a of the ink channels 107 located near the ball housing 103. Then, the liquid flows out through a gap around the ball 102 in the distal end 101 of the tip body 100. The liquid flows in the direction indicated by the arrow in FIG. 18 when the pen is in use.
The seat 105 of the ball housing 103 is processed by a so-called “tapping,” wherein the ball 102 inserted in the ball housing 103 is lightly pressed down (or tapped) toward the seat 105 on its head. This tapping causes the surface of the seat 105 to be concave so as to enable the ball 102 to rest on the seat 105 with a narrow gap between the ball 102 and the top open end of the tip body 100. In the case of a ball-point pen using water-based ink, the tapping takes place after the top open end at the distal end 101 of the tip body 100 is pressed.
The tip unit 120 is known, with the ball 102 being urged toward the distal end so as to prevent the liquid from leaking out. This ensures that when the applicator is not used, the ball 102 is urged by a spring toward the distal end, so as to be brought into full contact with the distal end 101 of the tip body 100, and when it is used (in writing), the ball 102 is pushed back toward the seat 105, so as to release the contact.
A liquid applicator such as a ball-point pen using the above-mentioned tip unit 120 is capable of writing with the liquid led out with the ball 102 pushed against the seat 105 and rotating. In some instances, an increased amount of liquid discharge is required.
In order to meet this requirement, the liquid passage from the capillary hole 110 to the distal end 101 of the tip body 1100 must be widened as much as desired.
However, as shown in FIG. 18, the liquid passage especially becomes narrow at three spots; that is, 1) near the outlet 107a of the ink channel 107, 2) near the spot at which the ball 102 is nearest a side wall 113 of the ball housing 103, and 3) near the gap around the ball 102 between the distal end 101 of the tip body 100.
More specifically, referring to FIG. 19, the tip unit 120 has three gaps T, S1, and S2. The gap T exists around the ball 102 near the outlet 107a of the ink channel 107, the gap S2 exists near the spot at which the ball 102 is nearest the side wall 113 of the ball housing 103, and the gap S1 exists near the gap around the ball 102 between the distal end 101 of the tip body 100. The ink passage becomes most narrow at these gaps T, S1 and S2.
As described above, the tapping takes place after the top open end at the distal end 101 of the tip body 100 is pressed and deformed. This tapping deforms the seat 105, thereby enabling the ball 102 to move in an axial direction (in a direction of ball displacement) as much as a deformed amount L. In this specification, “deform” or “deformation” does not mean that the object is spoiled but means that it is changed in shape.
In order to increase a liquid discharge rate, it is preferable to widen all the gaps S1, S2, and T, but it is difficult to widen both of the gaps S1 and T in the conventional liquid applicator, resulting in limiting an increased rate of liquid discharge.
The reason why both of the gaps S1 and T are hard to be widened simultaneously is as follows:
As mentioned above, since the distal end 101 is pressed toward the ball 102 so as to bring it into close contact with the ball 102, and then it is lightly tapped, the larger the deformed amount L is, the wider the gap S1 near the distal end of the tip body 100 becomes. However, as the deformed amount L is wider, the gap T near the outlet 107a around the ball 102 becomes narrower.
More specifically, as shown in FIG. 18, the outlet 107a of the ink channel 107 and thereabout is blocked by the ball 102 because of location of the seat 105, thereby reducing the size of the gap T. This reduction in size prevents the liquid from flowing through the gap T and thereabout.
The present invention is therefore to provide a tip unit for a liquid applicator with more constantly adequate discharge of liquid. The invention is also to provide a method of producing a tip unit that is readily produced.